Most integrated circuits are designed to carry a given, relatively small amount of current, on the order of about ten milliamperes. As the term is used herein, “integrated circuit” includes devices such as those formed on monolithic semiconducting substrates, such as those formed of group IV materials like silicon or germanium, or group III-V compounds like gallium arsenide, or mixtures of such materials. The term includes all types of devices formed, such as memory and logic, and all designs of such devices, such as MOS and bipolar. The term also comprehends applications such as flat panel displays, solar cells, and charge coupled devices.
When a current flow that is larger than that for which the integrated circuit is designed is passed through the circuit, the current flow tends to destroy various elements of the integrated circuit, such as gate dielectrics and junction, rendering it either unstable or inoperable. One source of excessive current flow is called electrostatic discharge. Electrostatic discharge is a general condition where a charge imbalance builds up over a period of time, caused by one or more of a variety of conditions, and then is suddenly released. The current flow, although extremely brief, can be quite high, such as on the order of about ten amperes, or about 10,000 times the normal operating current of an integrated circuit. Electrostatic discharge is not an uncommon occurrence in circuits. If unaccounted for in the design of integrated circuits, electrostatic discharge can potentially be a major cause of failure for integrated circuits.
Various methods and structures for the shunting of electrostatic discharge have been proposed. For example, shunting circuits operate to divert the current flow from an electrostatic discharge around the functional portions of the integrated circuit and through the shunt, which is designed to accommodate a larger current flow. Unfortunately, this method of protection requires the circuit designer to identify every circuit path that the discharge might follow, and insert an appropriate shunt around each such discharge path. Such shunts are placed in parallel to the circuits that they are designed to protect.
What is needed, therefore, is a system for inhibiting electrostatic discharge from damaging integrated circuits that overcomes problems such as those described above, at least in part.